The aim of this research is to investigate the developing axonal connections between the orbitofrontal cortex and basal ganglia and thalamus in the neonatal dog. Both lesion (Fink-Heimer method) and injections (3H-leucine and horseradish peroxidase) methods will be used to determine the spatial and temporal development of the axonal connections. Synaptogenesis will be examined with the electron microscope in both the caudate nucleus and mediodorsal thalamic nucleus. Golgi impregnation of neurons in the cerebral cortex, caudate nucleus, and mediodorsal thalamic nucleus will also be done to determine the degree of development of postsynaptic elements and their relationship to developing terminal fields. BIBLIOGRAPHIC REFERENCES: Tanaka, D., Jr. Thalamic projections of the dorsomedial prefrontal cortex in the rhesus monkey (Macaca mulatta), Brain Research 110:21-38, 1976. Tanaka, D., Jr. Orbitofrontal projections to the mediodorsal thalamic nucleus in the dog, Neuroscience Abstracts 2:129, 1976.